Royal Prussia in the context of "State of the Teutonic Order"

Nicolaus Copernicus (19 February 1473 – 24 May 1543) was a Renaissance polymath who formulated a model of the universe that placed the Sun rather than Earth at its center. The publication of Copernicus's model in his book De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres), just before his death in 1543, was a major event in the history of science, triggering the Copernican Revolution and making a pioneering contribution to the Scientific Revolution. Though a similar heliocentric model had been developed eighteen centuries earlier by Aristarchus of Samos, an ancient Greek astronomer, Copernicus likely arrived at his model independently.

Copernicus was born and died in Royal Prussia, a semiautonomous and multilingual region created within the Crown of the Kingdom of Poland from lands regained from the Teutonic Order after the Thirteen Years' War.

The Union of Lublin (Polish: Unia lubelska; Lithuanian: Liublino unija) was signed on 1 July 1569 in Lublin, Poland, and created a single state, the Polish–Lithuanian Commonwealth, one of the largest countries in Europe at the time. It replaced the personal union of the Crown of the Kingdom of Poland and the Grand Duchy of Lithuania with a real union and an elective monarchy, as Sigismund II Augustus, the last of the Jagiellons, remained childless after three marriages. In addition, the autonomy of Royal Prussia was largely abandoned. The Duchy of Livonia, tied to Lithuania in real union since the Union of Grodno (1566), became a Polish–Lithuanian condominium.

The Commonwealth was ruled by a single elected monarch who carried out the duties of King of Poland and Grand Duke of Lithuania, and governed with a common Senate and parliament (the Sejm). The Union is seen by some as an evolutionary stage in the Polish–Lithuanian alliance and personal union, necessitated also by Lithuania's dangerous position in wars with Russia.

Prussia (/ˈprʌʃə/; German: Preußen [ˈpʁɔʏsn̩] ; Old Prussian: Prūsija) was a German state centred on the North European Plain that originated from the 1525 secularization act of the Prussian part of the State of the Teutonic Order. For centuries, the House of Hohenzollern ruled Prussia, expanding its size with the Prussian Army. Prussia, with its capital at Königsberg and then, when it became the Kingdom of Prussia in 1701, Berlin, decisively shaped the history of Germany. Prussia formed the German Empire when it united the German states in 1871. It was de facto dissolved by an emergency decree transferring powers of the Prussian government to German Chancellor Franz von Papen in 1932 and de jure by an Allied decree in 1947.

The name Prussia derives from the Old Prussians who were conquered by the Teutonic Knights – an organized Catholic medieval military order of German crusaders – in the 13th century. In 1308, the Teutonic Knights conquered the region of Pomerelia with Danzig. Their monastic state was mostly Germanised through immigration from central and western Germany, and, in the south, it was Polonised by settlers from Masovia. The imposed Second Peace of Thorn (1466) split Prussia into the western Royal Prussia, a province of Poland, and the eastern Duchy of Prussia, a feudal fief of the Crown of Poland until 1657. After 1525, the Teutonic Order relocated their headquarters to Mergentheim, but managed to keep land in Livonia until 1561. The union of Brandenburg and the Duchy of Prussia in 1618 led to the proclamation of the Kingdom of Prussia in 1701.

Frederick II (German: Friedrich II.; 24 January 1712 – 17 August 1786) was the monarch of Prussia from 1740 until his death in 1786. He was the last Hohenzollern monarch titled King in Prussia, declaring himself King of Prussia after annexing Royal Prussia from the Polish–Lithuanian Commonwealth in 1772. His most significant accomplishments include military successes in the Silesian wars, reorganisation of the Prussian Army, the First Partition of Poland, and patronage of the arts and the Enlightenment. Prussia greatly increased its territories and became a major military power in Europe under his rule. He became known as Frederick the Great (German: Friedrich der Große) and was nicknamed "Old Fritz" (German: der Alte Fritz).

In his youth, Prince Frederick was more interested in music and philosophy than war, which led to clashes with his authoritarian father, Frederick William I of Prussia. However, upon ascending to the throne, he attacked and annexed the rich Austrian province of Silesia in 1742, winning military acclaim. He became an influential military theorist, whose analyses emerged from his extensive personal battlefield experience and covered issues of strategy, tactics, mobility and logistics.

The Polish Corridor (German: Polnischer Korridor; Polish: korytarz polski), also known as the Pomeranian Corridor, was a territory located in the region of Pomerelia (Pomeranian Voivodeship, Eastern Pomerania), which provided the Second Polish Republic with access to the Baltic Sea, thus dividing the bulk of Weimar Germany from the province of East Prussia. At its narrowest point, the Polish territory was just 30 km wide. The Free City of Danzig (now the Polish cities of Gdańsk, Sopot and the surrounding areas), situated to the east of the corridor, was a semi-independent German speaking city-state forming part of neither Germany nor Poland, though united with the latter through an imposed union covering customs, mail, foreign policy, railways as well as defence.

After Poland lost Western Pomerania to Germany in the late 13th century, the area of Eastern Pomerania with the strategically important port of Gdańsk remained a narrow strip of land giving Poland access to the Baltic Sea and was also sometimes referred to as Pomeranian corridor.